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<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=<device-width>, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        var a = function(){ return document.write("加了返回指令\n") }
        a()
        //这是
        var b = function(){ document.write("没加返回指令\n") }
        b()
        //
        
        document.write(a())
        //函数只要是要调用它进行执行的，都必须加括号。不加括号的，都是把函数名称作为函数的指针
    </script>
</body>
</html>